1. Field of the Invention
The present invention relates to a pneumatic tire that is suitable for a studless tire or the like, and can be improved in on-ice performance without exerting any influence on other tire performance.
2. Description of the Related Art
To achieve improvement of on-ice performance, studless tires have a large number of sipes on blocks or the like at a tread portion so as to increase a tread surface scratching force (edge effect) by the edges of the sipes. In addition, studless tires have a higher land ratio of a tread pattern to increase a ground-contact area and enhance a traction force with respect to an ice surface.
In recent years, for decreasing side slips on an icy road and enhancing grip performance on cornering (lateral grip performance), there has been demand that sipes be inclined in a tire axial direction so as to have a larger edge component in a circumferential direction thereof. However, as shown in FIG. 4, if an inclined angle θ of sipes “a” with respect to a tire axial direction is large, brock parts “b” divided by the sipes “a” become virtually small in thickness t, which leads to reduction in block rigidity, thereby resulting in deteriorated wear resistance, for example.
In light of such circumstances, the inventor of the subject invention has conducted research and revealed the following matters.
First, a center region of a tread portion on a tire equatorial plane side is under a higher ground-contact pressure compared with other regions. Accordingly, the center region delivers high levels of edge effect and traction force, which makes high contribution to on-ice performance. Therefore, it is possible to improve on-ice performance with a limited land ratio by increasing relatively a width of a center land portion disposed in the center region in the tire axial direction.
Next, it is possible to increase circumferential edge components and further improve on-ice performance by providing the center land portion with v-shaped grooves. This achieves further higher block rigidity and suppresses an adverse effect on other tire performance, such as deterioration in wear resistance, as compared with the case of providing the center land portion with inclined grooves, for example.